The present invention relates to systems for monitoring the performance of cardiac pacemakers and, more particularly, to a system within the implanted pacer for telemetering various functional parameters and a cooperating external system for sensing the telemetered information and presenting it in a read-out to the patient as well as transmitting it telephonically to a central monitoring station having means for analyzing and controlling the telemetering operation.
The telephone monitoring of pacemaker patients from centralized cardiac data centers has developed into a significant technology for improvement of patient safety. It is a particularly convenient means to determine the depletion of the pacemaker energy source so that elective reoperation can be performed prior to pacemaker failure. The remote monitoring systems presently in use transtelephone the pacemaker rate and the patient's ECG or peripheral pulse simultaneously to permit the determination of whether or not the patient's heart is responding properly to the pacemaker output pulse. The pacemaker's output pulse rate is usually made dependent upon its battery voltage so that the status of the battery can be determined from the patient's pulse rate. For the case of demand pacemakers that are inhibited by normal cardiac activity, remote monitoring requires assistance from the patient to induce a temporary pacemaker fixed rate mode. This procedure is accomplished by the patient's placing of an external permanent magnet over the pacemaker implant site. A magnetically operated reed switch within the pacemaker is employed to disrupt the normal cardiac sensing function and thereby force the pacemaker into a competitive fixed rate mode. Assessment of the battery voltage and pacemaker capture can be verified during the interval of the test.
While much progress has been made, it is still not possible with existing remote monitoring techniques, to assess the condition of the cardiac sensing threshold, the condition of the sensing circuitry, and a variety of vital timing functions. Additionally, the development of more complex pacemaker systems and functions has placed greater emphasis on the need to monitor the viability of these systems and functions.
Unfortunately, considerable restrictions are placed on remote pacemaker monitoring because of the required involvement of the patient. Patient skill, health, and safety are limiting factors in obtaining adequate remote tests of all vital pacemaker functions. Furthermore, with the development of advanced systems, the requirement for gathering adequate data during early clinical trials to prove efficacy prior to large scale marketing is limited by the techniques presently in use.
Advanced methods of monitoring vital pacemaker functions through the use of a special telemetry system contained within the implanted pacemaker are described in U.S. Pat. No. 4,026,305. That patent describes simple means to transmit data through the intact skin of the patient without requiring the use of the pacemaker pulse and/or patient pulse rate as the carrier of the information. By employing a patient pulse independent means to transmit the data, multiparameter monitoring at higher data rates is allowed, and a larger number of vital functions can be kept under surveillance.
An object of the present invention is to provide an improved system that will allow a remote operator to command the monitoring tests to be performed in order to minimize both the test time and the involvement of the patient in the monitoring activity and which permits remote monitoring of such internal pacer functions as hermetic integrity, current pulse, and load impedance.